1. Field of the Invention
The present invention generally relates to variable inductors, and more particularly, relates to variable inductors for use in mobile communications equipment and other such apparatuses.
2. Description of the Related Art
In electronic equipment, and in particular, in mobile communications equipment such as cellular telephones and car telephones, which are required to be miniaturized, the miniaturization of components used in such mobile equipment is also necessary. The higher the operating frequency, the more complicated the circuit configuration is. It is also required that the variation of characteristics of each component be reduced. However, variations do exist among components, so that a circuit including many such components may not function normally. To avoid such a problem, a variable component may be used for the components constituting the circuit. Characteristics of the variable component are adjusted, thus enabling the circuit to function normally. For example, a variable inductor with an inductance adjusting member (trimming pattern) has been used.
FIG. 8 is a perspective view of a conventional variable inductor with an inductance trimming member. An inductor 1 includes a spiral coil 3 on the surface of an insulating substrate 2. The inductance trimming member includes a plurality of electrodes 4 arranged in a ladder configuration. The inductance trimming member is disposed inside of the region where the coil 3 is provided. An end 3a of the coil 3 is electrically connected to an external electrode 7. Another end 3b of the coil 3 disposed on an insulating film 5 is electrically connected to an external electrode 8. The top surface of the variable inductor 1 is exposed to a laser beam, and the electrodes 4 are trimmed one by one. The inductance value between the external electrodes 7 and 8 is trimmed in a stepwise manner.
FIG. 9 is a perspective view of another conventional variable inductor 11. The inductor 11 includes a spiral coil 13 on the surface of an insulating substrate 12. An inductance trimming member includes leading electrodes 14a to 14d, which extend from the middle of the coil 13 to the outside of the region where the coil 13 is provided. The leading electrodes 14c and 14d are disposed on insulating films 15a and 15b. An end 13a of the coil 13 is electrically connected to an external electrode 17. Another end 13b of the coil 13 disposed on an insulating film 15c is electrically connected to an external electrode 18. The leading electrodes 14a to 14d are trimmed one by one, so that the inductance value between the external electrodes 17 and 18 is trimmed in stages.
The variable inductor 1 shown in FIG. 8 has the electrodes 4 disposed inside of the region where the coil 3 is provided, and the electrodes 4 interrupt a magnetic field generated by the coil 3. As a result, the Q -value of the inductor 1 is greatly decreased.
The variable inductor 11 shown in FIG. 9 includes the leading electrodes 14c and 14d opposed to the coil 13 with the insulating films 15a and 15b disposed therebetween, thus generating stray capacitance therebetween. An increase in the stray capacitance will result in a decrease in the resonance frequency. The trimming of the inductance value of the inductor 11 is performed at every turn, but fails to trim the inductance value precisely. Therefore, it is difficult to use the variable inductors 1 and 11 as trimming components for a high frequency circuit (in particular, a circuit requiring a high Q-value, such as a voltage controlled oscillation circuit).
In order to overcome the problems described above, preferred embodiments of the present invention provide a variable inductor having a high Q-value for trimming an inductance value.
According to a preferred embodiment of the present invention, there is provided a variable inductor including an insulating substrate, a coil provided on the insulating substrate, an inductance adjusting member provided on the insulating substrate and electrically connected to the coil, the inductance adjusting member is arranged to be trimmed to adjust an inductance value, and an external electrode provided on the insulating substrate, wherein the inductance adjusting member is disposed outside of an area where the coil is located.
The shape of the coil may preferably be spiral, meandering, or helical or other suitable shape.
The inductance adjusting member may be a ladder electrode, which preferably has a substantially L-shaped configuration on the insulating substrate.
Since the inductance adjusting member is disposed outside of the area where the coil is located on the substrate, the degree of interruption in which the inductance adjusting member interrupts a magnetic field generated by the coil is reduced, and an inductor having a high Q-value is obtained. The ladder electrodes of the inductance adjusting member are trimmed or cut one by one, thus trimming the inductance value in a stepwise manner.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.